The instant invention relates to color printing and more particularly relates to a single-pass multi-color thermal print engine.
Single-pass, multi-color electrostatic printers have heretofore been known in the art. In this regard, the U.S. Pat. Nos. 4,734,788 to Emmett et al; 4,804,979 to Kamas et al; and 5,006,868 to Kinoshita represent the closest prior art to the subject invention of which the applicant is aware.
The patent to Emmett et al discloses a single pass electrostatic color printer which has a straight paper path. The printer includes a continuous feed roll of paper which passes through a plurality of sequentially spaced electrostatic print stations. The paper is pulled through the printer by a drive roller located adjacent to the paper outlet. A pinch roller is associated with each print station wherein the pinch roller biases the paper against it's respective print station. Registration marks are printed along the lateral edges of the paper. The registration marks are read by optical sensors positioned at each print station. Using the data signals from the sensors, the printer continuously recalculates the correct printing position on the paper thus allowing the printer to compensate for shifting and stretching of the paper caused by the previous pinch roller.
The patent to Kamas et al discloses a single-pass multi-color printer/plotter incorporating four electrostatic print stations. The print stations are sequentially spaced along an elongated transport path, and each print station includes a transport roller system that allows the print media to traverse the print station with controlled force exerted on the media. The printer further includes a print registration system wherein each print station monitors registration marks to detect stretching or other deformations of the print media.
The patent to Kinoshita discloses a process for single-pass multi-color electrophotographic printing comprising the steps of forming first and second electrically charged oppositely polarized, latent images on a dielectric-covered photoconductive printing element. The printing process utilizes a Katsuragawa type, three layer photoconductive drum. During a single rotation of the drum two latent images are formed on the drum and thereafter first and second toners, oppositely charged and differently colored are applied to the first and second latent images, forming first and second toned images having different colors and different polarities. The toned images are then similarly charged and transferred to a print medium.